The release agent and mold temperature relationship

In die casting production process, mold release agent has been as an important means of mold cooling. Spraying water-based release agent, compressed air with release agent coating the mold surface at the same time, subjected to high temperature mold surface on their heating, and even make the release agent of water in contact with the mold surface yet have gasification, and along with the mold surface contact time, water-based releasing agent is heated at different temperatures, the mold is water-based release agent cooling degree is different. The process of heat transfer characteristics, analogous to heat transfer in boiling heat transfer, both nuclear boiling, and film boiling. As shown in the following illustration.

In the mold of hot, lubricant may be more affected by volatization ( volatilization temperature volatilization temperature ) or the effect of thermal gradient. If the cavity around the hot and cold zone temperature difference is large, then the surface tension gradient, lubricating film for Marangoni Effect ( in thermal physics called the horse pulled high, effector Marangoni Effect, i.e. when a liquid film under external perturbations, such as temperature, concentration, and make the film when the local thinning, it will be in the surface tension gradient is formed under the effect of the horse pulled high, flow, so that the liquid along the best route to the thin liquid, to" repair" ) will tend to flow to the mold cooler area. If the injection mold release agent sufficient to compensate Marangoni effect, the mold hot area completely covered, which could result in cold area has too many release agent, result in castings blowhole or stain. Conversely, if the injection mold release agent is not enough to compensate for the Marangon effect, then will lead to local membrane rupture. Visible, maintain the die temperature uniformity and die temperature appropriate for the release agent effectiveness of normal play is very important.

We can use the rough description of die casting production process painting release agent when the mold surface temperature change. In a die-casting aluminum alloy cyclic, shot before the mold surface temperature by forced cooling lowest can reach 205 degrees Celsius, but due to thermal conduction delay phenomenon and mold temperature control system, filling before the mold surface temperature of approximately 50-100 C rebound, which reached more about C 250-300. From the Aluminum castings alloy die casting solidification process requirements, general best mould temperature should be aluminum alloy mold filling temperature about 40%, therefore we design release agent chemical composition, usually selected the best application of mold temperature range is in 250-300 s. C. For example, our newly launched the third generation of the polymer as the matrix, mineral oil, environmental protection type release agent XY-70A, as long as the user can keep the stability of mold temperature in 250-300 s. C, the stripping effect is good, the casting surface is very bright, mold no carbon deposition, not sticking die, die service life improve. By casting the worker welcome.

But we from casting plant information feedback are also found, some die casting factory mold temperature in 300-350 s. C, even higher. They also use the XY-70A release agent, but not ideal, there will be die of carbon deposition. Apparently they must use to adapt to the higher temperature of the release agent, that is to say must be suitable is the best. And later switched to the appropriate temperature in 280-350 s. C XY-70B, effect is obviously improved. According to the North American Casting Association released data: for mold temperature control, according to the different spraying methods, mold internal cooling effect about 50-80%. Automatic spraying, can take approximately 40% more calories, manual spraying, can only take about 15% calories, with different operating habits have certain discrepancy, 85% rely on internal cooling and convection of heat. Visible, different press, different mold structure, different mold temperature control mode, resulting in different mold temperature difference, which may reach 121 degrees above C. Thus do not follow the same pattern, even with a new mold and die casting machine old because of mold temperature, on the release agent of the requirement and the use effect is also different.

That release agent problem position tend to occur in the mold surface heating the most intense or metal flow the strongest position. When the mold surface of the protective film is too thin or too loose and mold combination is prone to lead to the release of bad a series of troubles. The key is to maintain the mold temperature is as uniform as possible, so that the deposition on the surface of the mould release agent more uniform. Not all of the release agent are also in hot mold surface for forming good homogeneous membrane. The release agent in hot mold surface wetting and spreading ability depends on temperature and the release agent compositions. The aqueous release agent usually has a maximum acceptable mold temperature ( temperature ), the wetting and spreading the best performance. When the die temperature is higher, in Leiden the Frost effect ( Leidenfrost effect ) temperature, mold release agents cannot effective wetted surface. The effect that when the liquid temperature far above its boiling point ( such as water in the 200 - 300 DEG C ), liquid surface and vapor phases will form a thin layer, droplets can float on the layer and in which random sliding. This phenomenon is known as the" Leiden Frost effect. For a given release agent on its combustion temperature and Leidenfrost temperature depends on many variables, including the release agent composition, injection pressure, angle and the amount of. Gas pressure and release agent concentration effect. Despite releasing agent spraying parameters such as fluid pressure, spray angle and strength also influence the wetting and spreading properties, but the component plays the most important role.

Mold surface temperature are important factors affecting the adsorption effect. Too high too low to reduce the adsorption effect.

Low A value < 150 degrees C, spray paint rapidly so that the temperature is reduced to below water vaporization point, coating cannot be deposited onto the pressure surface, just from the surface of the die and a punch. Too much water carrier integrated in the cavity so that the casting produced by diffuse stoma.

B too high > 398 degrees C, sprayed coating is the mold surface of the vapor layer repulsion. Namely temperature has not been reduced to wetting temperature, only reaching the wetting temperature, spray paint droplets can be truly and pressure type surface contact, eventually forming a thin film.

For a given die temperature, considering the effect on the film formation influencing factors include droplet impact surface of the mold, wetting, spreading to form a continuous film, prevent subsequent spray wash. In addition there are many variables affecting the membrane formation. Including the spraying speed, spray gun and die surface angle, fluid pressure, spraying intensity, has formed on the membrane of the spraying angle. Release agent chemical application technology is the primary goal in the cavity formed on the surface of most effective membrane. The second is to achieve optimal mold cooling and minimal waste residue. Spraying equipment for continuous improvement and new release agent application technology makes mould lubrication closer to optimization. The die casting machine test to select the release agent is the traditional inspection methods. If the new release agent to use new old problem solving. While retaining the traditional method at the same time, Sand castings there are also some scientific display method. As in the mold is placed on thermocouple or infrared measuring device to measure and display the temperature of the mold at any time. In addition some methods are under development. Such as the measurement of core pulling stress, to judge from the difficulty of casting type. These results for the test performance and reasonable use of release agent to provide a more scientific basis.